Sudden unexplained death (SUD) remains a puzzle in forensic medicine. Desmoglein-2 (DSG2) has been linked to arrhythmogenic right ventricular cardiomyopathy which may cause life-threatening ventricular arrhythmias and sudden death. Fatal arrhythmias resulting in sudden death also occur in the absence of morphologic cardiac abnormalities at autopsy. We hypothesized that DSG2 mutations may be responsible for certain Chinese SUD cases. We sequenced all 15 exons of DSG2 in DNA extracted from postmortem heart tissues of 25 Chinese patients dying from SUD. The primers were designed using the Primer Express 3.0 software. Direct sequencing for both sense and antisense strands was performed with a BigDye Terminator DNA sequencing kit on a 3130 Xl Genetic Analyzer. Mutation damage prediction was made using Mutation Taster, PolyPhen, and SIFT software. In 2 of 25 cases of Chinese SUD samples, two DSG2 heterozygous mutations (p.P927 L and p.T1070M) were identified, and one is probably damaging. We concluded that DSG2 mutations may be related to the occurrence of part of SUD cases in the Chinese Han population.

Cases of sudden death in children and adults where no cause of death is found at autopsy may demonstrate morphologically normal myocardium. In this study, we used the term “sudden unexplained death (SUD)” while recognizing that it is a heterogeneous group of disorders and does not define a specific syndrome. SUD accounts for up to 30% of sudden death in adults, while the etiology of SUD remains unclear. Recently, SUD has been linked to ion-channel mutations in up to 25% of cases, indicating that some deaths from SUD are due to channelopathies.[1]

Normal heart function relies on correct electric and metabolic coupling between myocardial cells, which is accomplished by intercalated disc (ID), comprising desmosomes, gap junctions, and adherens junctions.[2] Desmosomes are intercellular adhesive complex formed by five major components, including desmoglein (DSG), desmocollin (DSC), plakophilins (PKP), plakoglobin (PG), and desmoplakin (DSP). Recently, mutations in desmosomal genes have been linked to arrhythmogenic right ventricular cardiomyopathy (ARVC),[3],[4],[5],[6],[7],[8],[9] which may cause life-threatening ventricular arrhythmias and sudden death.[10],[11]

In previous studies, we tested the plakophilin-2 (PKP2) and desmoglein-2 (DSG2) mutations, with heart tissue from patients dying of SUD in the Western population; 24% of SUD patients had PKP2 mutations[12] and 8% of SUD patients had DSG2 mutations,[13] which suggests that PKP2 and DSG2 mutations may result in SUD in the Western population. The goal of this current study was to evaluate the mutations in DSG2 from patients dying of SUD in the Chinese Han population.

Materials and Methods

Study subjects

Twenty-five cases dying from SUD were studied from the Department of Forensic Medicine, School of Basic Medical Sciences, Fudan University [Table 1]. The study has been approved by the Ethics Committee of Fudan University, and the international ethical guidelines have been followed during this study. All cases were seen in consultation with a cardiovascular pathologist and a forensic pathologist and examined in a similar fashion.

Genomic DNA was extracted from postmortem heart tissue using standard techniques.[14] All coding exons and flanking intronic sequences of DSG2 (NM_001943.3) were amplified by polymerase chain reaction (PCR). Primers and PCR conditions were available on request. The primers were designed using the Primer Express 3.0 software. Direct sequencing for both sense and antisense strands was performed with a BigDye Terminator DNA sequencing kit on a 3130Xl Genetic Analyzer (Applied Biosystems, Carlsbad, CA, USA). Data were analyzed using Lasergene software for the identification of mutations (DNASTAR, Madison, WI, USA). A control group of 100 healthy and unrelated individuals was used to exclude the possibility that the detected mutations were common DNA polymorphisms. Mutation damage prediction was made using Mutation Taster software (http://www.mutationtaster. org), Polyphen (http://genetics.bwh.harvard.edu/pph2), and Sorting Intolerant from Tolerant (SIFT) (http://sift.jcvi.org).

Results

Two DSG2 mutations have been identified in 2 of 25 SUD index cases (8%). Both of the two DSG2 mutations were heterozygous missense mutations. None of the detected nucleotide changes were found in the 100 control samples.

One of the missense substitutions was C2780T (P927 L) [Figure 1], considered to be probably damaging as analyzed by Polyphen, SIFT, and Mutation Taster. Another missense substitution was C3209T (T1070M) [Figure 2], considered to be benign as analyzed by Polyphen, SIFT, and Mutation Taster. Details regarding the identified mutations are summarized in [Table 2].

Sudden cardiac death (SCD) is the most common cause of death. Not all SCDs, however, have an obvious attributable cause that can be determined at autopsy. It is estimated that 10%–30% of sudden deaths have no identifiable fatal morphologic abnormalities found at autopsy, which is then labeled as autopsy negative or SUD.[15],[16],[17],[18],[19] Since the first ever report of a postmortem molecular diagnosis of long-QT syndrome (LQTS) through the use of a molecular autopsy occurred in 1999,[20] a considerable number of SUDs have been found to be associated with heritable cardiac channelopathies. These include LQTS – KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2; catecholaminergic polymorphic tachycardia – RyR2; and Brugada syndrome – SCN5A.[21],[22],[23],[24],[25] Benefiting from the developments in genome research, molecular autopsy may potentially provide a pathogenic basis for SUD and establish the cause and manner of death.

The structural and functional integrity of cardiomyocytes is supported by cell adhesion junctions in the ID, which contains the following three types of intercellular connection: gap junctions, adherens junctions, and desmosomes. The desmosome (macula adherens) is the morphologically most conspicuous cellular adhesion structure, providing mechanical attachment between the cells and is particularly abundant in tissues such as epidermis and myocardium that are continually assailed by mechanical forces. Desmosomes consist of three families of proteins, namely the armadillo family, PKP and PG, which contains armadillo repeat domains; the cadherin family consisting of transmembrane proteins responsible for anchoring the structure to the membrane, DSG and DSC; and the plakin family, DP.[26] Desmosomal armadillo interacts with cadherin proteins, which for their parts are connected to DP. The latter anchors desmosomes to intermediate filaments, mainly desmin, thereby forming a three-dimensional scaffolding that provides tissues with mechanical strength.[27],[28] Desmosomes are also believed to play an important role in cell–cell signaling themselves.[29] As the primary function of desmosomes is strong adhesion, it is not surprising that mutations in genes encoding desmosomal proteins are responsible for diseases in which cell adhesion is compromised, such as cutaneous disorders (palmoplantar keratoderma), multitissue syndromes, and ARVC.[30],[31]

ARVC is an inherited disease characterized by life-threatening ventricular arrhythmias, and the pathologic hallmark is fibrofatty replacement of cardiac myocytes.[10],[11],[32],[33] SCD is the first manifestation of ARVC in approximately one-fourth of patients,[11] and among the young, ARVC is a major cause of SCD.[34],[35] ARVC has been initially considered as a right-sided cardiomyopathy; however, a growing evidence supporting a concomitant or independent left ventricular arrhythmia is involved.[36],[37],[38],[39],[40],[41] A previous study which examined fifty cases of SCD with ARVC found that 50% involve both ventricles and 38% involve predominantly left ventricles,[42] similar to the clinical reports by Sen-Chowdhry et al.[37],[38]

In humans, there are four isoforms of DSG (DSG 1–4).[43] DSG2 is expressed in all desmosome-bearing tissues, including cardiac muscle.[44] Desmosomal gene mutations have been linked to ARVC,[3],[4],[5],[6],[7],[8],[9] and DSG2 is the fourth recognized desmosomal gene causing ARVC.[6],[44],[45] Approximately, 10% of patients with ARVC have mutations in DSG2.[6],[44],[45] Although ARVC is characterized by a structurally and functionally abnormal heart muscle, initial slight phenotypic alterations might not be visible at autopsy, making a proper diagnosis difficult.[46] We speculated that mutations in desmosomal genes could also be associated with arrhythmias in the absence of fibrofatty change of ARVC and may occur in cases of SUD. In fact, our previous studies have found PKP2 and DSG2 mutations in patients dying from SUD in the Western population.[12],[13] In the present study, we also found that 8% of patients dying of SUD in the Chinese Han population have DSG2 mutation. Both were heterozygous missense mutations; although their pathogenicity is uncertain, one missense mutation is probably pathogenic, according to Mutation Taster, Polyphen, and SIFT software. These aforementioned studies suggest that desmosome mutations may be related to the fatal arrhythmic events even in patients with a morphologically normal heart.

Conclusions

Our results demonstrate a link between DSG2 mutations and SUD cases in the Chinese Han population and have complication in that medical examiners who perform molecular genetic screening in cases of SUD need to be aware that DSG2 mutation may also be able to cause fatal arrhythmias even in patients with a morphologically normal heart.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Acknowledgments

This study was funded by the National Natural Science Foundation of China (NSFC fund: 81501630) and the Opening Project of Shanghai Key Laboratory of Crime Scene Evidence (No. 2016XCWZK20).

Financial support and sponsorship

This study was funded by the National Natural Science Foundation of China (NSFC fund: 81501630) and the Opening Project of Shanghai Key Laboratory of Crime Scene Evidence (No. 2016XCWZK20).

Ackerman MJ. State of postmortem genetic testing known as the cardiac channel molecular autopsy in the forensic evaluation of unexplained sudden cardiac death in the young. Pacing Clin Electrophysiol 2009;32 Suppl 2:S86-9.